1. Field of the Invention
The present invention relates to packages for housing pressure sensors, such as capacitive pressure sensors.
2. Description of the Related Art
In recent years, capacitive pressure sensors and piezoelectric pressure sensors have been developed, and these sensors are installed in devices of various types. When a sensor of such types is to be installed in a device, the sensor is usually packaged within a package, such as a ceramic package, before it is installed in the device.
Japanese Unexamined Patent Application Publication No. 9-101220 discloses an example of a pressure sensor packaged within a package. Specifically, when a pressure sensor is to be packaged within a package, an adhesive (die bonding agent) is applied entirely over the bottom surface of the package, and the pressure sensor is placed on the adhesive so that the pressure sensor is bonded (die-bonded) to the bottom surface of the package with the adhesive.
With the above-described installation technique, however, there are cases where a difference in thermal expansion coefficient between the material constituting the sensor and the material constituting the package has an effect on the sensor characteristics. For example, in a case where the sensor is composed of silicon and the package is composed of alumina, the thermal expansion coefficient of silicon is about 3 to 3.5×10−6/K, whereas the thermal expansion coefficient of alumina is about 8×10−6/K. Therefore, since the thermal expansion coefficient of the package is greater, the sensor may be adversely affected by thermal expansion of the package, leading to deterioration in the temperature characteristics of the sensor. In particular, in a pressure sensor in which a gap between a substrate and a diaphragm has a size of about several micrometers, the thermal expansion can cause the diaphragm to become deformed. In that case, the sensor becomes incapable of performing accurate pressure detection.